In a field of an on-vehicle interior lighting system, for example, it is proposed a bulb socket structure including: a resin-made socket main body for mounting a bulb such as a wedge base bulb; and a pair of power feeding terminals provided on the socket main body. A base portion of a bulb is inserted into a mounting hole in the socket main body, and the base portion is held between the pair of power feeding terminal (for example, see PTL 1). As shown in FIG. 8, in a bulb socket structure described in PTL 1, a pair of power feeding terminals 101 includes a pair of holding pieces 102 for holding a base portion 111 of a bulb 110 therebetween. When the base portion 111 is inserted into between the pair of holding pieces 102, the pair of holding pieces 102 is elastically deformed in a direction separating from each other, and a biasing force caused by the deformation holds the base portion 111, thereby the bulb 110 is held in the socket 100.